The field of art to which the invention pertains includes material handling storage racks having a vehicular restraint system associated therewith.
In order to conserve high cost floor space in warehouses and other storage buildings, material storage racks are located longitudinally closely adjacent one another so as to form very narrow aisles between rows of storage racks. The development of side-loader and order selector types of industrial trucks and stackers parallels the construction of very narrow aisle warehouses which has generated a requirement for mechanical constraints or guide means to insure vehicle movement in precise predetermined paths in the aisles between the rows of storage racks. The use of the narrowest possible aisle combined with vehicle guidance is advantageous both in maximizing the use of storage space, in insuring the capability of deposit and retrieval of loads from storage locations on both sides of the aisle without maneuvering the vehicle, and in eliminating any requirement for steering control by an operator, thereby permitting the operator to attend to other tasks.
Heretofore such vehicle guidance has been provided usually by the use of structural steel angle rails bolted to the floor along each side of each aisle and having installed low on each side of the guided vehicle pairs of side guide rollers in such a manner that when the vehicle is in the aisle the rollers contact the guide rails so that it is constrained to travel in a straight line between the rails.
A problem frequently encountered in the art concerns the provision of means for insuring without over stressing and damaging vehicle parts, the alignment of the vehicle for entry into such a guide rail system. This has been accomplished previously by such means as outwardly flared guide rail throats or entry ways at the head of each aisle so that during entry the vehicle is forcibly aligned to enter the straight-line portion of the aisle. Inherent in this solution is the problem of resisting the relatively high forces developed during a misaligned entry, particularly when the vehicle is heavily loaded. Such entry forces must be absorbed by the side guide rollers and means for mounting the rollers on the vehicle. Such forces are produced by initial impact of heavy vehicles with guide rails at entry sections, and by friction forces resulting from sliding such vehicles sideways to achieve initial alignment. One solution has been to use heavy springs to provide a resilient entryway for absorbing such forces, such as disclosed in U.S. Pat. No. 3,710,524. As a practical matter, however, the cost of such a construction in a typically large storage building is prohibitive.
My U.S. Pat. No. 3,850,111 discloses such a system in which the invention is directed to the construction and mounting of a guide plate assembly adapted particularly for material handling vehicles such as lift trucks.
Canadian Pat. No. 924,249, granted Apr. 10, 1973, discloses a materials storage frame supporting structure for use with automated storage and retrieval equipment in which floor mounted I-beams are utilized for providing tracks retaining roller mounted base structure of a material handling stacker machine and having vertical support posts of the storage frame structure supported from the upper flange of each I-beam which extends longitudinally of the aisle formed between the storage frame.
Side loading fork lift trucks such as is disclosed in my U.S. Pat. No. 3,850,111 utilize in such systems lift truck attachments capable of maneuvering palletized loads at various elevations in and out of bins on either side of the aisle and of actuating the pallet and load to a straight-ahead position on the attachment so that the truck may then travel to the end of the aisle and upon leaving the restraint system of the structure be maneuverable by the operator as desired. An exemplary side loader attachment is disclosed in U.S. Pat. No. 3,762,588. Usage of this type of truck is increasing as a result of the economies of handling materials in reduced aisle widths at increased stacking heights, the faster and more orderly handling of loads, and increased safety.
Operators of order selector trucks, on the other hand, ride on the lift platform to the various storage levels in the storage rack system and there select individual items. Stability or restraint against tipping forwardly or rearwardly in the aisle due to the application of brakes or acceleration of the truck is an important safety consideration. It is required that the travel speed of the truck be decreased as the lift carriage and loads are elevated, the deceleration being usually imposed electrically and automatically in such order selector trucks. As pay loads and storage heights in such systems increase, the vulnerability to tipping increases unless a satisfactory restraint system is utilized. Otherwise the productivity of both order selectors and side loader lift trucks is substantially reduced because of the necessity to operate at relatively low speeds when loads are elevated.